Due to their convenience of use, and also due to the increasing use of portable electrical and electronic apparatus, so-called rechargeable batteries or accumulators have become an established part of everyday domestic life.
These batteries or accumulators are devices for storing chemical energy and converting the chemical energy into electrical energy. Taking into account that their chemical content is rich in heavy metals, at the end of their life these batteries and accumulators have the disadvantage in that they are undesirable in urban garbage and a special treatment is required to remove all of the toxic elements.
Processes envisaged in the field of treatment of used batteries and accumulators must be able to deal with three characteristic aspects of the problem:
Quantitative aspect: the battery/accumulator market is in constant expansion. Today, it is estimated that it is necessary to treat 100 tons of batteries and accumulators per year per million population. One ton of batteries or accumulators represents on average 20,000 to 22,000 units. This treatment capacity should be increased by a factor of 3 by the year 2000.
Qualitative aspect: the complexity of the chemical aspect of the treatment problem can be appreciated from the below-indicated tabulation of the amounts of heavy metals for different batteries and accumulators of the usual types:
______________________________________ Zn MnO.sub.2 Hg Pb Cd Ag Ni Type % % % % % % % ______________________________________ Zinc-Carbon 17 29 0.01 0.1 0.015 -- -- Alkaline 14 22 0.3 0.05 -- -- -- Mercury Batteries 11 -- 33 -- -- -- -- Silver Batteries 10 -- 1 -- -- 10 -- Zn-Air Batteries 30 -- 1 -- -- -- -- Ni--Cd Accu. -- -- -- -- 15 -- 30 ______________________________________
Zinc-carbon and alkaline batteries account for 97% of today's market, and Ni--Cd accumulators vary from 0.5 to 2%. But the latter are expected to increase up to 5% in 3 to 5 years.
Purity aspect: a method of treating used batteries and accumulators is only technically and economically feasible if the resulting products can be recycled as primary products. The value of these recycled products is directly related to their degree of purity.
Different processes for treating used batteries and accumulators have been developed. The technology employed is either the thermic route, or the non-dry route by means of electrolysis. However, for both of these technologies, the minimum purity of the recycled products can only be reached in the absence of foreign elements, or in the presence of a minimal quantity thereof. For instance, thermic or electrolytic processes developed for recycling Ni--Cd accumulators can tolerate only 1% of zinc-based elements (alkaline or zinc-carbon batteries). In the other case, the thermic process used for alkaline or zinc-carbon batteries can tolerate only less than 1% of cadmium batteries.
The treatment of used batteries or accumulators from the public at large involves the problem that it is difficult or even impossible to envisage a selective collection according to the nature of the batteries or accumulators. A method of sorting these collected batteries or accumulators is thus becoming a vital necessity for the subsequent treatment processes.